1. Field of the Invention
The present invention is directed to an axial seal device and to an improvement in a rotary drill using an axial seal device and, more particularly, to an automatic wear compensating axial seal device which incorporates an elastic sealing member and an inclined surface on at least one of the members being sealed wherein the inclined surface and the elasticity of the sealing member combine to provide the wear compensation. Furthermore, the present invention is more particularly directed to a rotary drill bit which incorporates the improvement of this type of automatic wear compensating seal device.
2. Description of the Prior Art
In prior art devices where it is necessary to provide a seal between two elements which move relative to one another, the most common types of seals are annular seals such as those shown in U.S. Pat. No. 4,154,312 which is directed to a Barnetche drill bit, which is a rotary drill bit having a solid conical cutting head. The annular seal used in this reference are typical in that the annular sealing members are placed in grooves formed in one of the two members which are being sealed. The diameter of the annular sealing member is selected to be equal to the diameter of the groove so that the annular sealing member is not under any elastic force. The seal is formed by the peripheral surface of the annular sealing member which contacts the first member in the groove and the second member on the surface thereof. As a result of wear, the cross-sectional diameter of the seal will decrease, and eventually, the peripheral surface of the seal will not contact both the surface of the groove and the surface of the other element. At this point, the seal will lose its sealing effect.
Once the seal has lost its sealing effect then harmful elements in the environment, in which the sealed device is operating, can enter the interior of the device causing damage to other parts of the device. In a device such as the rotary drill bit shown in U.S. Pat. No. 4,154,312, the portion of the drill bit which wears first is the seals. In order to replace the seals, it is necessary to withdraw the drill bit from a bore hole, remove the cutting head, add new seals, replace the cutting head and then place the drill bit down the bore hole again. This is a time consuming task and, therefore, the change of the seals is a costly operation as a result of the lost time. Furthermore, failure to change the seals can cause serious damage to the internal elements of the drill bit.
Another type of prior art seal is a helical spring or bellows seal. This type of seal provides wear compensation since the sealing surfaces are perpendicular to the axis of the helical spring or bellow and the helical spring or bellow are compressed in order to bias the seal surfaces together and it also provides a large sealing surface. Although this type of seal is effective since it provides compensation for wear, the sealing devices are complicated and costly and further they require a relatively large amount of space. Space becomes a significant factor when the surfaces being sealed are used in a very small place such as a bore hole for a drill.